Common fluorescent lights flashing with a commercial AC power source repeatedly blink at a cycle of 1/100th of a second and 1/120th of a second when the frequency of the power source is 50 Hz and 60 Hz, respectively. When such incident light is converted into an electrical signal and read by an image pickup device, an exposure initiation time is varied with the position of the readout pixel when an image pickup tube or a MOS type solid-state image sensing device is used, as a result of which the total sum of the amount of light entering within the exposure time of each pixel is varied even in the same frame. As a result, a single frame has a bright portion and a dark portion at the cycle of 1/100th of a second or 1/120th of a second, and such a phenomenon is called flicker.
Japanese Patent Laid-Open Publication No. 2002-152604 discloses a flicker removal device for extracting a luminance component from a video signal output from a solid-state image sensing device, and detecting flicker based on the extracted luminance component, thereby controlling the exposure time of the solid-state image sensing device based on a result of detection.
Japanese Patent Laid-Open Publication No. 2004-153710 discloses an imaging device for performing control in the following manner in order to speed up initial correction control, such as exposure and white balance control. That is, the imaging device rapidly reads out image data capable of forming one field from a CCD as two items of divided image data, and uses one of the divided image data items to perform initial correction control of, for example, exposure in accordance with the imaging condition. It also produces image data for one field using two divided image data items to display an image on a viewfinder.
The luminance level of a fluorescent light whose power source frequency is 50 Hz, for example, indicates repetitive blinking at a cycle of 1/100th of a second as described above. Accordingly, when the exposure period of the solid-state image sensing device is set at 1/100th of a second or an integral multiple thereof, the luminance level of the video signal read out at that timing is averaged, wand so flicker may not be detected.
In the imaging device disclosed in Patent Document 2, however, the exposure period for the divided image data items is preferably the exposure period appropriate for displaying an image on a viewfinder. Consequently, when flicker is detected by the flicker detection means disclosed in Patent Document 2 based on the divided image data items used for displaying an image on a viewfinder, flicker of a desired light source may not be detected.